Fault indicator providing contact closure on fault detection

ABSTRACT

A fault indicator for detecting the occurrence of a fault current in a monitored conductor includes a rotatably mounted indicator flag. The flag is positioned in either a reset indicating or a fault indicating state by a magnetic pole piece, which is magnetized in one magnetic direction or the other by momentary application of a current in one direction or the other to an actuator winding on the pole piece. An auxiliary magnetic circuit comprising an auxiliary pole piece magnetized by the actuator winding, a reed switch and a bias magnet magnetically aligned to oppose the reset magnetic orientation and reenforce the trip magnetic orientation of the magnetic pole piece provides contact closure upon occurrence of the fault current.

BACKGROUND OF THE INVENTION

The present invention relates generally to current sensing devices forelectrical systems, and more particularly to resettable alternatingcurrent fault indicators.

Various types of self-powered fault indicators have been constructed fordetecting electrical faults in power distribution systems, includingclamp-on type fault indicators, which clamp directly over cables in thesystems and derive their operating power from inductive coupling to themonitored conductor, and test point type fault indicators, which aremounted over test points on cables or associated connectors of thesystems and derive their operating power from capacitive coupling to themonitored conductor. Such fault indicators may be either of the manuallyreset type, wherein it is necessary that the indicators be physicallyreset, or of the self-resetting type, wherein the indicators are resetupon restoration of line current. Examples of such fault indicators arefound in products manufactured by E. O. Schweitzer Manufacturing Companyof Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477,4,063,171, 4,234,847, 4,375,617, 4,438,403, 4,456,873, 4,458,198,4,495,489, 4, 4,974,329, and 5,677,678 of the present inventor.

Detection of fault currents in fault indicators is typicallyaccomplished by means of magnetic switch means such as a magnetic reedswitch in close proximity to the conductor being monitored. Uponoccurrence of an abnormally high fault-associated magnetic field aroundthe conductor, the magnetic switch actuates a trip circuit whichproduces current flow in a trip winding to position an indicator flagvisible from the exterior of the indicator to a trip or fault indicatingposition. Upon restoration of current in the conductor, a reset circuitis actuated to produce current flow in a reset winding to reposition thetarget indicator to a reset or non-fault indicating position.

In certain applications the need arises for indicating or recording thedetection of a fault current at a location remote from the faultindicator. For example, where fault indicators are installed in each ofmultiple distribution circuits fed from a common source, it may bedesirable to monitor the fault indicators at a central monitoringfacility to enable a fault to be quickly isolated. Repair crews can thenbe efficiently designated to the known location of the fault.

Because of the compact construction and limited power available inself-powered fault indicators it is preferable that the auxiliarycontacts require minimal additional circuitry and structure within thefault indicator while providing reliable contact closure upon occurrenceof a fault. The present invention is directed to a novel contactarrangement which meets the above requirements by utilizing a magneticwinding, such as the actuator winding of the electro-mechanicalindicator flag assembly typically utilized in fault indicators, inconjunction with a magnetic circuit to actuate a magnetically biasedreed switch to provide contact actuation upon occurrence of a fault.

Accordingly, it is a general object of the present invention to providea new and improved fault indicator having auxiliary contacts forsignaling fault occurrence.

It is a more specific object of the present invention to provide a newand improved self-powered fault indicator which provides contact closureupon occurrence of a fault current in a monitored conductor.

It is a still more specific object of the present invention to provide afault indicator wherein a fault-indicative contact closure is providedutilizing the electro-magnetic flag indicator assembly of the faultindicator.

SUMMARY OF THE INVENTION

The invention is directed to a fault indicator for indicating theoccurrence of a fault current in an electrical conductor, wherein thefault indicator comprises a housing, a magnetic circuit including amagnetic pole piece, a magnetic actuated switch and a bias magnet, thebias magnet having a magnetic polarity which opposes a magnetic field inthe magnetic pole piece in one direction, and reenforces a magneticfield in the magnetic pole piece in the other direction, whereby themagnetically actuated switch is conditioned to a reset indicating statein response to a magnetic field in the one direction and to its faultindicating state in response to a magnetic field in the other directionand means including a magnetic winding in magnetic communication withthe magnetic pole piece and responsive to the current in the monitoredconductor for developing a magnetic field in the magnetic pole piecedirection to condition the switch in its reset indicating positionduring normal current flow in the monitored conductor, and fordeveloping a magnetic field in the pole piece in the opposite directionto condition the switch in the fault indicating position upon occurrenceof a fault current in the conductor.

The invention is further directed to a fault indicator for indicatingthe occurrence of a fault current in an electrical conductor, whereinthe fault indicator comprises a housing, an indicator flag assemblyincluding an indicator flag viewable from the exterior of the housingand a first magnetic pole piece, the indicator flag being magnetized andin magnetic communication with the first pole piece whereby theindicator flag is actuated to a reset-indicating position by a magneticfield in the first magnetic pole piece in one direction, and is actuatedto a fault-indicating position by a magnetic field in the first magneticpole piece in the opposite direction, a second magnetic circuitincluding a second magnetic pole piece, a magnetically actuated switchand a bias magnet, the bias magnet having a magnetic polarity whichopposes a magnetic field in the second magnetic pole piece in onedirection, and reenforces a magnetic field in the second magnetic polepiece in the other direction, whereby the magnetically actuated switchis actuated to one state in response to a magnetic field in the onedirection and to its other state in response to a magnetic field in theother direction, and means including a magnetic winding in magneticcommunication with the first and second magnetic pole pieces andresponsive to the current in the monitored conductor for developing amagnetic field in the one direction in the pole pieces to position theindicator flag in the reset indicating position and condition themagnetically actuated switch in the first state during normal currentflow in the monitored conductor, and for developing a magnetic field inthe opposite direction to the pole pieces to position the indicator flagin the fault indicating position and condition the magnetically actuatedcontacts in the second state upon occurrence of a fault current in theconductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with the further objects and advantages thereof, may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings, in the several figures ofwhich like reference numerals identify like elements, and in which:

FIG. 1 is a perspective view of a inductively powered clamp-on faultindicator constructed in accordance with the invention installed on acable within a power distribution system.

FIG. 2 is a top plan view of the fault indicator of FIG. 1 showing theengagement between the fault indicator and the cable.

FIG. 3 is a cross-sectional view of the fault indicator of FIGS. 1 and 2taken along line 3--3 of FIG. 2.

FIG. 4 is a cross-sectional view of the fault indicator of FIGS. 1-3taken along line 4--4 of FIG. 3.

FIG. 5 is a perspective view, partially in section, showing theprincipal components of the indicator flag assembly utilized in thefault indicator of FIGS. 1-4.

FIG. 6 is a cross-sectional view of the indicator flag assembly takenalong line 6--6 of FIG. 5.

FIG. 7 is an enlarged cross-sectional view of the auxiliary contacts ofindicator flag assembly taken along line 7--7 of FIG. 5.

FIG. 7A is a cross-sectional view of the indicator assembly taken alongline 7A--7A of FIG. 7.

FIG. 7B is a cross-sectional view of the indicator assembly taken alongline 7B--7B of FIG. 7.

FIGS. 8A and 8B are diagrammatic views of the principal components ofthe indicator flag assembly of the fault indicator in a reset indicatingposition.

FIGS. 9A and 9B are diagrammatic views similar to FIGS. 8A and 8B,respectively, showing the principal components of the indicator flagassembly in transition between a reset indicating position and a faultindicating position.

FIGS. 10A and 10B are diagrammatic views similar to FIGS. 8A and 8B,respectively, showing the principal components of the indicator flagassembly in a fault indicating position.

FIG. 11 is an electrical schematic diagram of the circuitry of the faultindicator module shown in FIGS. 1-5.

FIG. 12 is a view similar to FIG. 7 showing an alternate orientation ofthe magnetically actuated reed switch of the fault indicator of FIGS.1-11.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the Figures, and particularly to FIG. 1, a clamp-oncurrent-reset fault indicator 20 constructed in accordance with theinvention for indicating fault currents in an electrical feeder ordistribution cable 21 is seen to include a circuit module 22 and anintegral indicator module 23. The indicator module 23 projects from thefront face of the circuit module so as to be easily viewed when thefault indicator is installed. In accordance with conventional practice,the circuit module is attached to the outer surface of cable 21, whichmay include a central conductor 25, a concentric insulating layer 26,and an electrically-grounded rubber outer sheath 27.

Basically, circuit module 22 includes a housing 30 within whichcircuitry for sensing fault currents and actuaing indicator module 23 iscontained, and a magnetic core assembly 31 for attaching the module to amonitored conductor (such as cable 21) and for providing sufficientmagnetic coupling to the conductor to power the circuitry of the circuitmodule. The core assembly is preferably formed as a closed loop ofgenerally rectangular configuration so as to completely encircle cable21, and includes a gap 32 by which the core can be opened to facilitateinstallation on or removal from a monitored conductor. A hook 33 on thecore and an eye 36 on housing 30 may be provided to allow use of aconventional hotstick during installation or removal. A spring 34 holdsthe gap closed and presses the monitored cable 21 into a V-shaped recess35 on housing 30.

The indicator module 23 includes, in accordance with conventionalpractice, a status-indicating flag 40 for indicating circuit status. Theflag 40 may be viewed through a window 41 at the front of the indicatormodule.

In operation, during normal current flow in conductor 21, indicator flag40 is positioned by circuitry in circuit module 22 so as to present awhite or reset condition-indicating surface 40A to the viewer. Upon theoccurrence of a fault current in the conductor, the indicator flag isrepositioned by the circuitry so as to present a red or fault-indicatorsurface 40B to the viewer.

Referring to FIG. 2, the core assembly 31 of circuit module 22 mayconsist of a plurality of individual strips or laminations formed oforiented silicon steel arranged side-by-side in a generally rectangularclosed-loop configuration. The core assembly is preferably encapsulatedin a layer of resin epoxy insulating material. The rectangularconfiguration includes a generally rectilinear first or left sideportion 42, a generally rectilinear second or right side portion 43opposed to first portion 42, a generally rectilinear third or bottomportion 44 and a generally rectilinear fourth or top portion 45 opposedto third portion 44. The closed loop consisting of side portions 42-45includes gap 32 at the juncture of left side core portion 42 and bottomcore portion 44. The left side portion 42 is drawn toward the right sideportion 43 by biasing means in the form of helical spring 34 whichextends between the two opposite sides of the core.

To provide operating power for the fault indicator circuit module 22includes a magnetic winding 50 in operative association with magneticcore assembly 31. As shown in FIGS. 2 and 3, winding 50 is coaxiallypositioned on the bottom portion 44 of the core assembly and isdimensioned to provide a close fit with the core cross section. Thewinding is preferably connected to a circuit board 51 on which the othercomponents of the circuit module are mounted. These components include amagnetic reed switch 52, which is positioned with its axis perpendicularto and spaced from the axis of conductor 21 so as to respond to faultcurrents in the conductor in a manner well known to the art. The entireassembly, consisting of winding 50, circuit board 51, magnetic reedswitch 52 and the other components of the module, may be encapsulated inan epoxy material 53 so as to form within housing 30 at the bottomportion of core assembly 31 a weatherproof module responsive to thecurrent level in conductor 21.

Referring to FIG. 5, indicator module 23, which may be conventional instructure and operation, includes a cylindrical transparent plastichousing 60 within which the components of the module are contained.Within housing 60 an integral partition 61 serves as a mask and spacingelement, and a transparent end cap 62 sonically welded to the end of thehousing seals the interior against contamination while providing theviewing window 41 (FIG. 1).

A disc-shaped circuit board 63 is positioned perpendicularly to the axisof the housing. This circuit board, which may be secured in position byan epoxy material filling the rear portion of the housing, serves asmounting means for the components of the indicator module.

To provide an indication of the occurrence of a fault current, theindicator module includes within the lower end of housing 60 thegenerally disc-shaped indicator flag 40 mounted for rotation about apivot axis 66. As best seen in FIGS. 8-10, the face of target indicator40 has a red segment 40B and a white segment 40A, only one of which isvisible at a time through window 41 in the transparent end of housing60.

Secured to and pivotal with indicator flag 40 is a permanent flag magnet67 which is formed of a magnetic material having a high coercive force,such as ceramic, and is magnetically polarized to form two magneticpoles of opposite polarity, as indicated in FIGS. 8-10, with oppositemagnetic polarities along a diameter of the magnet.

A pole piece 68, which is preferably formed of a magnetic materialhaving a relatively low coercive force, such as chrome steel, in a resetcondition is biased at its projecting ends to the magnetic polaritiesindicated in FIGS. 8A and 8B. As shown in FIG. 5, the ends of the polepiece extend along the side wall of housing 60, in close proximity toflag magnet 67. As a result, the opposite polarity magnetic poles offlag magnet 67 are attracted to position the indicator flag 40 to thereset or non-tripped position shown. In this position the red segment40B of the indicator flag is not visible through window 41, and all thatis seen is white segment 40A.

On the occurrence of a fault current in conductor 21 pole piece 68 isremagnetized to the magnetic polarities shown in FIGS. 9 and 10 bymomentary energization in one direction of a winding 70 on the centersection the pole piece. As a result, the poles of magnet 67 are repelledby the adjacent like-polarity poles of the pole piece and indicator flag40 is caused to rotate 180° to its tripped position, as shown in FIGS.10A and 10B. In this position, the red segment 40B of indicator flag 40is visible through window 41, and a lineman viewing the fault indicatoris advised that a fault current has occurred in the conductor.

Indicator flag 40 remains in its fault indicating position until theends of pole piece 68 are subsequently remagnetized to the magneticpolarities shown in FIGS. 8A and 8B, by momentary energization ofwinding 70 with a current in the opposite direction. Upon thishappening, indicator flag 67, and hence indicator flag 40 is caused torotate from the tripped position shown in FIGS. 10A and 10B to the resetposition shown in FIGS. 8A and 8B, and the fault indicator isconditioned to respond to a subsequent fault current.

To preclude indicator flag 40 from becoming stalled upon reversal of themagnetic polarities of pole piece 68, as might happen with a targetperfectly centered between the poles of the pole piece and having adegree of bearing friction, the fault indicator includes an auxiliaryU-shaped pole piece 71 positioned adjacent target magnet 67 coaxial withand at an angle to pole piece 68. The existence of a magnetic fieldbetween the poles of pole piece 68 results in the production of inducedmagnetic poles in auxiliary pole piece 71. As a result, upon reversal ofthe magnetic polarity of the poles of pole piece 68 following occurrenceof a fault current the auxiliary poles exert a rotational force on themost adjacent poles of the target magnet 67. This causes a rotationalmoment to be exerted on flag indicator 40 tending to turn the flag in apredetermined (counter-clockwise in FIGS. 8-10) direction such that theflag is precluded from remaining in its reset position, even if itshould be perfectly positioned and have a degree of bearing friction.Once rotation has been established, as shown in FIGS. 9A and 9B, thegreater force of the main pole piece 68 overcomes the effect of theauxiliary pole piece 71 and rotation continues until the flag is alignedas shown in FIGS. 10A and 10B.

Energization of winding 70 by current in one direction upon occurrenceof a fault current in conductor 21, and energization of winding 70 bycurrent in the opposite direction upon restoration of current inconductor 21, is accomplished by means of circuitry contained withincircuit module 22. Referring to the schematic diagram shown in FIG. 11,the single winding 70 of indicator module 23 is connected to the circuitmodule by conductors 74 and 75.

Power for operation of the circuit module is obtained from pick-upwinding 50, within which an alternating current is induced in a mannerwell known to the art as a consequence of alternating current inconductor 21. Winding 50 is tuned to resonance at the power linefrequency by a capacitor 80 and the resultant resonant output signal ispeak-limited by a pair of zener diodes 81 and 82 connected back-to-backacross the winding.

The resonant signal is increased in voltage by a conventional voltagemultiplier circuit comprising diodes 83-86 and capacitors 87-90 todevelop in a manner well known to the art a direct current of sufficientmagnitude for powering the circuitry of the module.

The positive polarity output terminal of the voltage multiplier network,formed at the juncture of diode 83 and capacitor 88, is connected to oneterminal of winding 70 through a conductor 91, and to one terminal of afirst current storage capacitor 92. The negative polarity outputterminal of the voltage multiplier network, formed at the juncture ofdiodes 86 and capacitor 90, is connected to the remaining terminal ofcapacitor 92, and through a forward-biased diode 93 and a currentlimiting resistor 94 to one terminal of a second current storagecapacitor 95. The other terminal of capacitor 95 is connected to theremaining terminal of winding 70 through a conductor 96. With thisarrangement, capacitor 92 is charged directly, and capacitor 95 ischarged through winding 70, by the unidirectional current developed bythe voltage multiplier network during normal current flow in conductor21.

To provide for periodic energization of winding 70 during normal currentflow in conductor 21, the remaining end terminal of winding 70 isconnected through a first switch device in the form of a siliconcontrolled rectifier (SCR) 97 to the negative polarity terminal ofcapacitor 92. Periodic conduction through SCR 97 is obtained byconnecting the gate electrode of that device to the positive polarityoutput terminal of the voltage multiplier network through a voltagedivider network comprising a pair of resistors 98 and 99 and a bilateraldiode 100. SCR 97 is periodically triggered into conduction when thevoltage developed across bilateral diode 100 as a result of capacitor 97being charged by the voltage multiplier network reaches the thresholdlevel of the diode. This causes a current flow in a first direction inwinding 70, with the result that indicator flag 40 is positioned asshown in FIGS. 8A and 8B. Diode 93 prevents capacitor 95 from beingdischarged through SCR 97 upon conduction of that device, leaving thecapacitor available for energizing winding 70 in a reverse direction inresponse to a fault condition.

Winding 70 is energized in the reverse direction upon occurrence of afault current in conductor 21 by discharge of capacitor 95 through asecond SCR 101 having its cathode connected to the negative polarityterminal of the capacitor, and its anode connected to the first endterminal of winding 70. Conduction is established through SCR 101 byclosure of the contacts of reed switch 52, which is connected betweenthe positive polarity terminal of capacitor 95 and the gate electrode ofSCR 101 by a network comprising a resistor 102 and a capacitor 103, abilateral diode 104, and a resistor 105.

Reed switch 52 is positioned within housing 30 in sufficiently closeproximity to conductor 21 such that the contacts of the switch closeupon occurrence of a fault current in the conductor. Upon thisoccurrence, the positive polarity terminal of capacitor 95 is connectedthrough the closed contacts of reed switch 52 and the circuit comprisingresistors 102 and 105, bilateral diode 104, and capacitor 103 to thegate electrode of SCR 101, causing that device to be renderedconductive. This causes capacitor 95 to discharge through the SCR,energizing winding 70 in the reverse direction and repositioningindicator flag 40 as shown in FIGS. 10A and 10B.

To preclude the possibility of currents of opposite direction beingapplied to winding 70 by simultaneous conduction of SCR 101 and SCR 97,a predetermined time delay in conduction through SCR 101 may be providedfollowing occurrence of a fault current in conductor 21. This isaccomplished by resistor 102 and capacitor 103, which together form anRC time constant network in the gate circuit of SCR 101. Upon closure ofthe contacts of reed switch 52 it is necessary that capacitor 103 chargethrough resistor 102 to the threshold voltage of bilateral diode 104before sufficient gate electrode current is supplied to SCR 101 toinitiate conduction in that device. Resistor 105 serves in aconventional manner as a current drain path for the gate electrode.

The time delay provided is designed to insure that should a fault occursimultaneously with the periodic energization of winding 70 in a resetdirection, capacitor 92 will have completely discharged prior to winding70 being energized to signal the fault.

Thus, in operation winding 70 is supplied with unidirectional current inone direction from a first current storage device, capacitor 92, and inan opposite direction from a second current storage device, capacitor95. Capacitor 92 is connected to one terminal of the magnetic winding,and capacitor 95 is connected to the other terminal. A first switchdevice, SCR 97, periodically completes the discharge circuit forcapacitor 92 to the opposite terminal of the winding during resetconditions. A second switch device, SCR 101, completes the dischargecircuit for capacitor 95 to the opposite terminal of the winding uponthe occurrence of a fault current.

The two current storage capacitors 92 and 95 are simultaneously chargedby a charging circuit which includes the line current-powered voltagemultiplier network. Capacitor 92 is charged directly and capacitor 95 ischarged through winding 70, isolation diode 93 and resistor 94. Diode 93provides isolation for the trip circuit upon operation of the restcircuit.

In accordance with the invention, an auxiliary contact closure isobtained in fault indicator 20 upon occurrence of a fault current inmonitored conductor 21 by providing a second magnetic circuit inindicator module 22. In particular, and referring to FIGS. 5 and 8-10,the second magnetic circuit is formed by a second U-shaped magnetic polepiece 110, a reed switch 111 and a bias magnet 112. Pole piece 110, likepole piece 68, is preferably formed of a magnetic material having arelatively low coercive force, such as chrome steel. Winding 70 wrapsaround both pole piece 68 and pole piece 110, so that the direction ofthe magnetic field induced in both pole pieces is dependent on thedirection of current in the winding. The lead wires of reed switch 111are positioned in close proximity to the ends of pole piece 110 tocomplete the magnetic circuit. However, to avoid a short circuit acrossthe switch the lead wires are electrically isolated from the pole piecesand are connected by lead wires 113 and 114 of a cable 115 to anexternal location for signaling and/or control purposes.

In operation, when fault indicator 20 is in a reset state with indicatorflag 40 positioned as shown in FIG. 8A, and the magnetic circuit throughreed switch 111 is as shown in FIG. 8B. In the absence of bias magnet112 the magnetic field between the poles of pole piece 110 would causethe contacts of reed switch 111 to close. However, bias magnet 112 ispolarized to oppose the magnetic poles as now polarized so that thefield between the poles is sufficiently weakened so that the reed switchcontacts do not close and no fault is signaled.

Upon occurrence of a fault, the polarity of the magnetic poles of polepiece 110 changes, as shown in FIGS. 9B and 10B, and magnet 112 works tostrengthen the magnetic field applied to the reed switch contacts. Thecontacts now close, signaling a fault.

To prevent undesired actuation of reed switch 111 from the externalmagnetic field associated with conductor 25 the switch is preferablyaligned with its axis generally parallel to the axis of the monitoredconductor. In this case, to avoid actuation of the switch by the straymagnetic field of winding 50, the reed switch 111 is preferablycontained within a cylindrical sleeve 116 of magnetically conductivematerial, such as copper, with bias magnetic 112 being positioned on theoutside surface of the sleeve with its axis parallel-spaced to the axisof the reed switch. However, where the monitored conductor issufficiently spaced from the reed switch that the magnetic field of theconductor is not a factor, the reed switch can be aligned with its axisperpendicular to the axis of the actuator winding 70 as shown in FIG. 12to minimize the effect of winding 70 on the reed switch. In this casethe cylindrical magnetic shield 116 may not be required.

The leads of reed switch 111 can be magnetically coupled to andelectrically isolated from the magnetic poles of pole piece 110 bysoldering or otherwise attaching the switch leads to metallic sleeves117, which are fitted over sleeves 118 of electrically insulatingmaterial, such as vinyl, which in turn are fitted over the magneticpoles.

It will be appreciated that while the auxiliary contact arrangement ofthe invention has been shown incorporated in an inductively coupledcurrent powered fault indicator, the inventive arrangements finds equalutility in capacitively coupled electrostatically powered faultindicators such as those mounted on system test points.

Thus, a compact externally-powered fault indicator has been describedwhich upon sensing of a fault current provides a contact closure forexternal signaling and control purposes. By utilizing the existingelectro-mechanical indicator flag assembly, a minimal number ofadditional components are required, making the device especially wellsuited for economically upgrading existing fault monitoring systems.

While a particular embodiment of the invention has been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made therein without departing from theinvention in its broader aspects, and, therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of the invention.

I claim:
 1. A fault indicator for indicating the occurrence of a faultcurrent in an electrical conductor, comprising:a housing; a magneticcircuit including a magnetic pole piece, a magnetic winding, amagnetically actuated switch, and a bias magnet, said bias magnet havinga magnetic polarity which opposes a magnetic field in said magnetic polepiece in one direction, and reenforces a magnetic field in said magneticpole piece in the other direction, whereby said magnetically actuatedswitch is conditioned to a reset indicating state in response to amagnetic field in said one direction and to a fault indicating state inresponse to a magnetic field in said other direction; and circuit meansincluding said magnetic winding and responsive to the current in themonitored conductor for developing a magnetic field in said pole piecein said one direction to condition said magnetically actuated switch insaid reset indicating position during normal current flow in themonitored conductor, and for developing a magnetic field in said polepiece in said other direction to condition said magnetically actuatedswitch in said fault indicating position upon occurrence of a faultcurrent in the conductor.
 2. A fault indicator as defined in claim 1wherein said magnetic pole piece includes a pair of spaced-apartmagnetic poles, and said magnetically actuated switch is disposedbetween said poles.
 3. A fault indicator as defined in claim 2 whereinsaid magnetically actuated switch includes a pair of projecting leads,and said leads are mechanically connected to but electrically isolatedfrom said magnetic poles.
 4. A fault indicator as defined in claim 3wherein said magnetically actuated switch comprises a reed switch.
 5. Afault indicator as defined in claim 4 wherein the axis of said reedswitch is aligned generally parallel to the axis of said monitoredconductor.
 6. A fault indicator as defined in claim 5 wherein saidmagnetic pole piece is generally U-shaped.
 7. A fault indicator forindicating the occurrence of a fault current in an electrical conductor,comprising:a housing; an indicator flag assembly including an indicatorflag viewable from the exterior of the housing and a first magnetic polepiece, said indicator flag being magnetized and in magneticcommunication with said first magnetic pole piece whereby said indicatorflag is actuated to a reset-indicating position by a magnetic field insaid first magnetic pole piece in one direction, and is actuated to afault-indicating position by a magnetic field in said first magneticpole piece in the opposite direction; a magnetic circuit including asecond magnetic pole piece, a magnetically actuated switch and a biasmagnet, said bias magnet having a magnetic polarity which opposes amagnetic field in said second magnetic pole piece in one direction, andreenforces a magnetic field in said second magnetic pole piece in theother direction, whereby said magnetically actuated switch is actuatedto a reset-indicating state in response to a magnetic field in said onedirection and to its fault-indicating state in response to a magneticfield in said other direction; and circuit means including a magneticwinding in magnetic communication with said first and second magneticpole pieces and responsive to the current in the monitored conductor fordeveloping a magnetic field in said one direction in said magnetic polepieces to position said indicator flag in said reset indicating positionand condition said magnetically actuated switch in said reset-indicatingstate during normal current flow in the monitored conductor, and fordeveloping magnetic fields in said opposite direction in said magneticpole pieces to position said indicator flag in said fault indicatingposition and condition said magnetically actuated switch in saidfault-indicating state upon occurrence of a fault current in theconductor.
 8. A fault indicator as defined in claim 7 wherein saidsecond magnetic pole piece includes a pair of spaced-apart magneticpoles, and said magnetically actuated switch is disposed between saidpoles.
 9. A fault indicator as defined in claim 8 wherein saidmagnetically actuated switch includes a pair of projecting leads, andsaid leads are mechanically connected to but electrically isolated fromsaid magnetic poles.
 10. A fault indicator as defined in claim 9 whereinsaid magnetically actuated switch comprises a reed switch.
 11. A faultindicator as defined in claim 10 wherein the axis of said reed switch isaligned generally parallel to the axis of said monitored conductor. 12.A fault indicator for indicating the occurrence of a fault current in anelectrical conductor, comprising:a housing; a rotatably mountedindicator flag viewable from the exterior of said housing; a firstmagnetic pole piece having magnetic poles in magnetic communication withsaid indicator flag, said flag assuming a reset-indicating position inresponse to a magnetic field in said first magnetic pole piece in onedirection and a trip-indicating position in response to a magnetic fieldin said first magnetic pole piece in the other direction; a magneticallyactuated switch; a second magnetic pole piece having magnetic poles inmagnetic communication with said magnetically actuated switch, and abias magnet opposing a magnetic field in said second magnetic pole piecein said one direction and reenforcing a magnetic field in said secondmagnetic pole piece in said other direction whereby said magneticallyactuated switch is actuated to a reset indicating state in response tomagnetic field in said one direction and to a fault indicating state inresponse to magnetic field in said second magnetic pole piece in saidother direction; and circuit means including a magnetic actuator windingin magnetic communication with said first and second magnetic polepieces for inducing magnetic fields in said one direction in said polepieces when said fault indicator is in a reset state, and in said otherdirection when said fault indicator is in a trip state.
 13. A faultindicator as defined in claim 12 wherein said second magnetic pole pieceincludes a pair of spaced-apart magnetic poles, and said magneticallyactuated switch is disposed between said poles.
 14. A fault indicator asdefined in claim 13 wherein said magnetically actuated switch includes apair of projecting leads, and said leads are mechanically connected tobut electrically isolated from said magnetic poles of said secondmagnetic pole piece.
 15. A fault indicator as defined in claim 14wherein said magnetically actuated switch comprises a reed switch.
 16. Afault indicator as defined in claim 15 wherein the axis of said reedswitch is aligned generally parallel to the axis of said monitoredconductor.
 17. A fault indicator as defined in claim 12 wherein saidfirst and second magnetic pole pieces are generally U-shaped.
 18. Afault indicator as defined in claim 17 wherein said actuator winding iswound on the transverse portion of said U-shaped first and secondmagnetic pole pieces.